Allow custom types to define their own serialization with __str__.

PiperOrigin-RevId: 260078541
Change-Id: I2999e0caaaf962708ab1de4272b1df58327b2ada

docs/guide.md

@@ -413,7 +413,7 @@ if __name__ == '__main__':
 Now we can draw stuff :).
 
 ```bash
-$ python example.py move 3 3 on move 3 6 on move 6 3 on move 6 6 on move 7 4 on move 7 5 on __str__
+$ python example.py move 3 3 on move 3 6 on move 6 3 on move 6 6 on move 7 4 on move 7 5 on
 0 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0 0
 0 0 0 0 0 0 0 0 0 0
@@ -428,6 +428,16 @@ $ python example.py move 3 3 on move 3 6 on move 6 3 on move 6 6 on move 7 4 on
 
 It's supposed to be a smiley face.
 
+### Custom Serialization
+
+You'll notice in the BinaryCanvas example, the canvas with the smiley face was
+printed to the screen. You can determine how a component will be serialized by
+defining its `__str__` method.
+
+If a custom `__str__` method is present on the final component, the object is
+serialized and printed. If there's no custom `__str__` method, then the help
+screen for the object is shown instead.
+
 ### Can we make an even simpler example than Hello World?
 
 Yes, this program is even simpler than our original Hello World example.

docs/using-cli.md

@@ -91,6 +91,8 @@ the arguments of the class's \_\_init\_\_ function. Arguments must be specified
 by name, using the flags syntax. See the section on
 [calling a function](#calling-a-function) for more details.
 
+Similarly, when passing arguments to a callable object (an object with a custom
+`__call__` function), those arguments must be passed using flags syntax.
 
 ## Using Flags with Fire CLIs <a name="using-flags"></a>
 

fire/core.py

@@ -244,6 +244,15 @@ def _PrintResult(component_trace, verbose=False):
   # and move serialization to its own module.
   result = component_trace.GetResult()
 
+  if hasattr(result, '__str__'):
+    # If the object has a custom __str__ method, rather than one inherited from
+    # object, then we use that to serialize the object.
+    class_attrs = completion.GetClassAttrsDict(type(result))
+    str_attr = class_attrs.get('__str__')
+    if str_attr and str_attr.defining_class is not object:
+      print(str(result))
+      return
+
   if isinstance(result, (list, set, frozenset, types.GeneratorType)):
     for i in result:
       print(_OneLineResult(i))
@@ -253,9 +262,6 @@ def _PrintResult(component_trace, verbose=False):
     print(_DictAsString(result, verbose))
   elif isinstance(result, tuple):
     print(_OneLineResult(result))
-  elif isinstance(result, complex):
-    # Print "3+4j" instead of "(3+4j)".
-    print(str(result).strip('()'))
   elif isinstance(result, value_types.VALUE_TYPES):
     if result is not None:
       print(result)

fire/inspectutils.py

@@ -98,7 +98,6 @@ def Py2GetArgSpec(fn):
 
 def GetFullArgSpec(fn):
   """Returns a FullArgSpec describing the given callable."""
-
   original_fn = fn
   fn, skip_arg = _GetArgSpecInfo(fn)